Process for lithium soap greases



United States Patent Oflice 3,388,065 Patented June 11, 1968 3,388,065 PROCESS FOR LITHIUM SOAP GREASES Roland N. Haimhaugh, Munster, Ind., assignor, by mesne assignments, to Sinclair Research, Inc., New York, N.Y., a corporation of Delaware No Drawing. Filed Aug. 5, 1965, Ser. No. 477,609 3 Claims. (Cl. 252-42.1)

ABSTRACT OF THE DISCLOSURE This invention is directed to an improvement in the manufacture of lithium soap greases which contain as their essential thickening ingredient a lithium soap from the glyceride of 12-hydroxy stearic acid.

Greases thickened with the lithium soap from the glyceride of l2-hydroxy stearic acid have become of increasing commercial importance, particularly because of their value as so-called multi-purpose greases and as high quality greases for certain heavy duty performance conditions. One method of preparing these lithium greases, and the method with which the present invention is concerned comprises saponifying the fatty component, that is, the glyceride of 12-hydroxy stearic acid, with an aqueous lithium hydroxide in the presence of at least a portion of the total mineral oil base to be used in the grease composition, dehydrating the mixture at a maximum temperature below the melting temperature of the soap, e.g. up to about 370 F., adding any additional amount of oil needed to formulate the grease, and, if desired, colloidally milling or other-wise homogenizing the grease to provide the finished product. The finished grease usually contains about '5 to 25 weight percent soap, at least 50%, preferably at least 80%, by weight, of which is the lithium soap from the glyceride of l2-hydroxy stearic acid. Thus, a minor portion, preferably about to 20% of the soap content of the greases can be of lithium soaps of another grease-making fat, fatty acid or other soap-forming organic acids. The glyceride of 12-hydroxy stearic acid is commercially available in the form of hydrogenated castor oil.

Although lithium greases prepared as described above provide excellent service, they may form a dark deposit when used at elevated temperatures. It has been found that the deposit formation is caused primarily by the presence of both free lithium hydroxide and glycerine. Ordinarily, the presence of at least about 0.06% by weight free lithium hydroxide and the glycerine resulting from the saponification, which is often at least about 0.5% by weight, is necessary before the appearance of deposit formation. For example, lithium greases made from 12- bydr-oxy stearic acid or its esters of monohydric alcohols rather than of glycerine, do not give deposits. Also,

lithium greases made in the manner that leaves very little free lithium hydroxide, usually less than about 0.06% by Weight in the finished grease, do not exhibit a deposit problem.

We have now discovered that the deposit problem caused by the glycerine and free lithium hydroxide in the lithium greases made from the glycerides of 12-hydroxy stearic acid can be eliminated by adding back to the grease after dehydration, a small amount of water sufficient to bring the total water content of the finished lithium grease to 0.2 to about 0.5%, preferably 0.20 to 0.35% by weight. The dehydrated grease generally contains up to 0.1% water and the amount of water added back is thus at least about 0.1% by weight. All of these percentages are based on the finished grease although at the time of water add back all of the components of the final grease, e.g. the finishing oil, may not be present.

The lithium grease of the present invention can be made in conventional steam-jacketed kettles at moderate maximum kettle temperatures of the order of about 250 to 370 F., preferably about 300 to 350 F. In the process of manufacture, the glyceride of 12-hydroxy stearic acid and part or all of the mineral oil base are charged to the kettle, the initial oil being at least about 20% of the total oil. Advantageously, the initial oil is about 50 to of the total oil. The mixture of glyceride and oil is usually brought to about 180 to 190 F., to melt the glyceride before charging the lithium hydroxide, the lithium hydroxide is added in the form of a boiling aqueous solution of lithium hydroxide or lithium hydroxide monohydrate and the saponification is effected by agitating the mixture of oil, glyceride and base, for instance, at a temperature of about 180 to 220 F., for, say about 20 to 30 minutes. The mixture is then dehydrated by raising the temperature to about 250 F. to 370 F., preferably about 300 to 350 F. After dehydration has been effected, the grease is cooled by reducing the temperature to about to 200 F, preferably about to F., for instance, by adding the finishing oil. After this cooling the grease usually will have a water content of below 0.1% by weight. The add-back water is combined with the grease when the latter is at a temperature low enough so that the added water will not evaporate. Since this added water should be mixed into the grease, I prefer to add the water into the kettle before the grease is colloid milled or homogenized.

The colloid milling operation is subject to considerable flexibility in control. The variables include inlet temperature, rate of throughput and mill clearance, with decrease in all three tending to increase the yield or the thickening of fat. The colloid mill clearances ordinarily vary from about 0.003 to 0.040 inch, preferably 0.005 to 0.010. A temperature rise during milling of about 20 to 25 F., is often experienced and may be controlled by use of cooling water in the jacket of the colloid mill. The operation is usually once through, but multi-pass milling may be employed. If desired, any of the additives conventionally incorporated into lithium greases can be added to the mixture of the present invention before colloid milling. These additives include for example, antioxidants, extreme pressure agents, dyes and etc.

The mineral oil base employed in the preparation of the lithium greases of the present invention is of lubricating viscosity and is preferably a mineral oil having a viscosity 3 of about 65 SSU at 100 F., up to a viscosity of about 175 SSU at 210 F. For heavy duty automative greases, a mineral oil having a viscosity of about 75 to 100 SSU ties and the results of the tests including worked penetration, WP, and unworked penetration UNWKD, in strokes are shown in Table I below.

Shell Roller (R.T.) Hours. Shell Roller (180 F.) Hours 1 Deposit in cup. 2 Deposit in cup and shaft. 3 No deposit.

4 Deposit.

5 Heavy deposit.

at 210 F. is preferred. The mineral oils of course, may be The data of Table I illustrate that the adding back to refined, e.g. by solvent treatment, hydrogenation or acid the lithium grease of small amounts of water provides an treating. A particularly preferred base oil is a blend of Mid-Continent neutral oil and bright stocks.

The following example is included to further illustrate the present invention, but is not to be considered limiting.

Example I A grease of the type modified by the present invention can be made by employing a 62:38 parts blend of a solvent refined Mid-Continent neutral oil, 200 SSU at 100 F., 95 VI, and a Mid-Continent bright stock, 150 SSU at 210 F. Four parts of the oil blend and one part of hydrogenated castor oil can be charged to a steam-jacketed grease kettle and thoroughly mixed at 180 F., until all the hydrogenated castor oil has melted, whereupon a slight excess of lithium hydroxide monohydrate as a 16% solution in water can be added. The mixture is then stirred and heat applied to dehydrate the product at a maximum tempreature of 350 F. to an anhydrous condition. The heat can then be turned off and four parts of oil added with stirring. When the grease has cooled down sufiiciently, additives such as anti-oxidants can be incorporated. The grease can then be processed at 170 F. through a colloid mill, set at 0.005 inch clearance.

Several batches of greases were prepared employing the identical compositions and the same procedure except that in some cases after cooling of the grease prior to its processing through the colloid rnill, a small amount of water, as indicated in Table I below, was added back to the grease. Each of the grease batches prepared was tested in the Shell Roll Tester for deposit formation. The Shell Roll Tester was run at room temperature and at 180 F. Deposit formation was also observed in the ASTM Worker after working 100,000 strokes. Physical propereffective method of preventing deposit formation without adversely effecting the desirable properties of the lithium grease.

It is claimed:

1. In the manufacture of a lithium grease of a mineral oil base, by saponifying the glyceride of 12-l1ydroxy stearic acid with an aqueous lithium hydroxide in the presence of at least a portion of the total base oil to be used in the grease composition, dehydrating the mixture at a maximum temperature of up to about 370 F., adding any additional amount of base oil needed to formulate the grease, said grease containing about 5 to 25 weight percent soap and at least about 0.06% free lithium hydroxide, the improvement which consists essentially of adding to the grease after dehydration at least about 0.1 weight percent water, based on the final grease composi' tion, and sufiicient to bring the total water content of said finished grease to 0.2 to 0.5% by weight.

2. The process of claim 1 wherein the glyceride of 12- hydroxy stearic acid is hydrogenated castor oil.

3. The process of claim 1 wherein the amount of water added is about 0.2 to 0.35% by weight.

References Cited UNITED STATES PATENTS 2,450,254 9/1948 Puryear et al. 252-41 2,898,298 8/1959 Zweifel et al. 252-41 3,117,087 1/1964 McCormick et al. 252-41 DANIEL E. WYMAN, Primary Examiner.

I. VAUGHN, Assistant Examiner. 

